Artificial joints generally utilize a variety of mechanisms to control their movement and to provide support and stability. Specifically an artificial knee joint needs to bend or articulate during sitting, kneeling or ambulating. By providing improved control of the leg during the swing-phase of the gait when the person is walking or running, one also improves the look of the gait and makes the gate look more natural.
Improved support and stability when one is standing or putting weight on the leg is critical during the support-phase or stance-phase of the gait cycle otherwise the artificial joint may bend uncontrollably causing the amputee to fall. Amputees have some control during stance by the way they load the leg and how they use their remaining muscles at the hip. Alternatively, a prosthetist can align a prosthesis to be more or less stable by placing the knee joint axis behind the load bearing plane or load line. However, this tends not to produce ideal gait characteristics.
Many different designs for artificial knee joints have been proposed to address the issue of support/stance-phase control, including a built-in “locking” mechanism for this purpose. Typically, these designs are joints which lock manually during ambulation so that the person has a choice of walking with his leg locked in extension or in a free swing. If the locked position is chosen, the person is forced to walk stiff legged. However, as noted above flexing at the knee during walking may result in uncontrollable movement and a buckling of the person's leg.
Artificial joints with automatically engaging locking mechanisms also have some major disadvantages. One disadvantage in current automatic locking mechanisms is that the automatic locking can occur only when the user has achieved full extension of the knee. The timing of the locking can cause an accident for the person as they may not be able to fully extend the knee before loading or placing weight on the leg. This would result in the knee to fold uncontrollably and allow the person to fall as noted above. Another disadvantage relates to the fact that although the locking mechanism automatically locks, these joints require manual operation to disengage or unlock the joint. This in turn requires that the user must have a free hand to activate the disengagement mechanism and could discourage the user from the therapeutic bending of the knee.
Prior art artificial joints have been devised to address some of the noted problems. For example, US Patent Application 2002/0183673 A1 by Naft discloses an electromechanical orthotic knee joint. It uses sensors that electronically provide signals to actuate a magnetic coil that brings together a set of serrated disks, thus preventing flexion. U.S. Pat. No. 5,267,950 issued to Weddendorf on Dec. 7, 1993 discloses an orthotic knee joint mechanism that under loading presses a set of bevelled serrated members into a bevelled surface, thus locking the knee. When unloaded the surfaces are not engaged and flexion/extension at the knee joint is possible.
Thus an artificial joint with a locking mechanism which provides improved stabilization and support while at the same time providing unrestricted motion is desirable.